The Spectre/Meltdown Performance Impact On Linux 4.20, Decimating Benchmarks With New STIBP Overhead

Like with the Core i9 tests, the impact of Spectre/Meltdown mitigations are very noticeable for the memcached mcperf benchmark.

That's where the dual Intel Xeon server I frequently for use for benchmarking stands as of the latest Linux 4.20 Git code. It's quite surprising to see the additional performance overhead now presented by this new kernel code due to STIBP. We'll see what performance optimizations come about still for the Linux 4.20 cycle (if any) pertaining to this cross-HT Spectre V2 mitigation. Hopefully these tests will apply some extra urgency and pressure for optimizations as when this code was added during the Linux 4.20 cycle it did so without too much attention yet the performance impact is glaring.

We'll also see if AMD ends up needing STIBP or what's up on that front among other benchmarks to come in the days ahead. Fortunately even if the STIBP overhead can't be improved too much, at least Intel is closing in on the Cascade Lake Xeon launch where they are introducing new hardware-based Spectre and Meltdown mitigations. If you want to maximize your system/server performance today, the mitigations can be disabled if you so choose.

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